Streptococcus sanguis and S. mutans were grown in the continuous mode both singly and in coculture. The results showed that S. sanguis had a higher affinity for glucose used as a limiting energy source than S. mutans. S. mutans, however, appeared to produce an inhibitor to S. sanguis. When S. mutans is inoculated first in the continuous culture, it remains the dominate organism after subsequent inoculation of S. sanguis. We have continued to accumulate data on the chemical composition of oral bacteria which have been grown in highly controlled conditions of pH and nutrient composition.